Shielded spark plug



March 3l, 11953 M INGRAM 2,633,116

SHIELDED SPARK PLUG 8f-.- I6 f Q I9 INVENToR.

MAXWELL INGRAM Hen. e BY/,MMMW

March 31, 1953 M |NGRAM 2,633,116

SHIELDED SPARK PLUG Filed'NQv. 2, 1949 2 SHEETS- SHEET 2 MAXWELL INGRAM INVENTOR.

Patented Mar. 31, 19t-"i3 SHIELDED SPARK PLUG Maxwell Ingram, Dumont, N. J., assigner, by mesne assignments, to Leonard Spark Plug Co., Inc., a. corporation of New Jersey Application November 2, 1949, Serial No. 125,108

This invention relates to new and useful improvements in a spark plug, and more particularly to a spark plug enclosed in a metallic shield.

It is an object of this invention to provide a spark plug with efcient shielding means for the purpose of preventing the radiation of electrical interferences from the spark formed therein in order to avoid interferences with the operation of radio and electronic equipment.

1t is a further object of this invention to provide a spark plug having a shielding and cover assembly which may be readily and disengageably assembled and which is formed of parts capable of being eiiiciently and economically manufactured and assembled.

It is an additional object of this invention to provide a shielded spark plug arrangement wherein the high and low potential sections of said plug are adequately isolated and insulated from one another in such manner as to provide against the formation of leakage paths therein.

Another object of this invention is to provide a shielded spark plug arrangement wherein the entrance of moisture which might impair the operation of said plug is largely prevented and wherein means are provided for entrapping such moisture as may find its way into said plug.

It is a further object of this invention to provide a spark plug arrangement of the shielded variety wherein air spaces are so formed as to provide for a more even distribution of the heat engendered therein thereby preventing the impairment vof the operation of said plug or the rupture of ceramic insulating means provided therein.

Another object of this invention is to provide said spark plug with ecient means for assuring electrical continuity between the sections of the high potential electrode positioned therein and the ignition `cable connected thereto.

A still further object of this invention is to provide a shielding cap arrangement for said plug formed of two sections of insulating material surrounded by a one piece shell which may therefore be of sheet metal and which may be readily assembled and sealed and is adapted to retain a section of the high potential electrode as well as an ignition cable connected thereto in a convenient position.

A still further' object of this invention is to (Cl. 12S-169) provide a shielding cover arrangement for said plug wherein an ignition cable may be readily connected to the high potential electrode thereof and provision is made for eilicient insulation between the shielding portion of said cover and the high potential elements retained therein.

An additional object of this invention is to provide said plug with positive and negative cooperating electrode surfaces such that a highly eiicient spark area is produced thereby.

Other and further objects of this invention will become apparent from the description thereof contained in the annexed speciiications, or will otherwise become obvious. It will be understood that the invention here disclosed may be employed for other purposes to which the structure and arrangement are adapted.

Figure 1 is a side elevation of said shielded spark plug,

Figure 2 is a cross-section of the spark plug shown in Figure 1,

Figure 3 is a fragmentary view of a portion of the cover of the shielded spark plug, partly in cross-section showing a modiiied arrangement for securing an ignition cable therein, and

Figure 4 is a fragmentary view of the spark plug showing a modified form of means for disengageably securing the shielding cover in position.

The spark plug comprising the present invention is illustrated in Figure 1 of the drawings and comprises a body shell Il which is secured to an intermediate body shield l2 and surmounted by a shielding cover I3 in engagement with said intermediate shield. A terminal tube I4 is provided on said cover to permit the entry of an ignition cable l5 therein. Ground and center electrodes are shown at I6 and I1 respectively.

As is more particularly shown in Figure 2, body shell H forms the main supporting body for said spark plug. Said shell is formed of metal and is provided with a lower portion of reduced diameter on which threads i3 are formed for the purpose of permitting the attachment of said plug to the body of an internal combustion engine and is well known in the art. Depending from said lower portion of the shell is ground electrode I6. Said electrode may be formed of an electrically conductive solid bar or wire of square or rectangular cross section, it having been found advantageous to form said electrode so as to present a plane upper surface i9 to the face of the complementary center electrode I7 as will more clearly appear hereafter. Although the ground electrode may be formed integrally with the shell, it has been found advantageous to form these elements separately and then weld them to each other. It should also be noted that the ground electrode I3 is oriented at an angle with respect to the plane of the lower end surface of said shell. As a result of the reduction in diameter in the lower portion of the shell, a shoulder 2u is formed thereon which is adapted to be seated upon an engine block or cylinder head. Gasket 2i is interposed between said elements in order to provide for a gas tight seal between the engine and the spark plug as well as for the purpose of providing a desirable thermal and electrical conductive path therebetween. Shell l! is further provided with an internal annular shoulder 22 whereon main body insulator` 23 is adapted to be seated, as will more clearly appear hereafter.

Principal insulation between the grounded portions of said spark plug and the high voltage portions thereof is accomplished by means of main body insulator 23. Said insulator is formed of a ceramic or similar insulating material and is positioned within shell Il. The diameter of the insulator is enlarged at 2d as a result of 'f which upper and lower annular shoulders 25 and 23 respectively are formed thereon. Gasket 2'! is interposed between shoulder 22 on the shell and the lower shoulder 26 on the insulator; a

similar gasket 28 being seated upon upper shoulder 25. Insulator 23 is rmly secured in position in shell i l by the clamping action of intermediate shield l2. The shield is provided with a threaded lower portion which terminates in a beveled end 30 adapted to be seated upon gasket" 23. Upon the threaded engagement of the internal threads on shell H with the external threads on the lower portion of the shield as shown at 29, the insulator is clamped tightly into position; the gaskets serving to provide gas tight seals as well as heat conducting paths from the insulator to the engine body and external atmosphere through the shell and shield. A hexagonal or similar surface may be provided upon a portion of the shell and shield as shown at 3i l for the purpose of permitting said elements to be clamped tightly and to be mounted on an engine block by means of wrenches or similar tools.

Insulator 23 is provided with an axial bore 32 which is enlarged and threaded at 33 and further enlarged to form cavity 34. Positioned within axial bore 32 is center electrode I1 which is provided with a threaded upper portion 35 whereby it is secured in position in the insulator. A

small gasket adapted to be firmly seated at the l lower end of the enlargement in axial bore 32 l being beveled as shown at 38 thereby presenting an oval or elliptical solid surface area to the ground electrode of substantially greater area than the normal cross section thereof. As has fheretofore been indicate-d ground electrode i3 presents a plane upper surface I9; said surface l lies in a plane parallel to the plane 0f the ellipti- 4 cal surface of the center electrode. As a result of this arrangement the electrodes present substantial parallel solid surface areas to each other and produce a larger and more uniformly distributed spark area between the electrodes. The formation of both the ground and center electrodes from solid material provides good thermal conductivity to carry away and distribute the heat of the spark.

Center electrode il is further provided with a flange 39 which seats upon the lower rim of the wall of cavity 34 and determines the degree to which the electrode is extended through the bore of the insulator thereby determining the spacing between the electrodes. Said ange also acts to complete the seal between bore 32 in the insulator and the center electrode. Boss dii is formed on the upper end of the center electrode and is adapted to be surrounded by helical spring lll which is seated on flange 39. The lower convolutions of spring 4l are engaged in the threads formed on boss 49. The upper convolutions of said spring are formed with a larger diameter in order to permit the free action of said spring' in spite of variations in the degree of compression k0f -said spring.

vis provided between the helical spring and the center electrode.

Intermediate shield l2 is formed of an elec trically conductive metal and adapted to be threadedly engaged with shell Il as has heretofore been indicated thereby forming a continuous conductive path with said shell and serving to clamp insulator 23 in position. The lumen ,of the interior of the shell and shield is greater than the outer diameter of the insulator thereby forming an air space between said elements.. It should be noted thatsaidspace is enlarged at the upper portion lof thefshield, as shown at d2. It has been found that the upper portion of the ceramic insulator is frequently liable to rupture due to the inequality inl temperature between the upper and lower portions thereof. As a result of the arrangement herein provided an air column exists along a substantial portion of the insulator thereby accomplishing a more equal distribution of heat along the length thereof as a result of the convection currents set up in said air column. Cracking of the insulator from this cause is therefore largely reduced. l. .v

The space between the meeting surfacesofthe shield and cover may be' such as to form a capillaryv path for moisture. In order to prevent the entrance of moisture into the interior ofthe plug by this means, the space between lsaid meeting surfaces is enlarged at theupper edge vof the shield. Thus the outer and end surfaces of the upper edge, of the shield are beveledvor tapered as shown at 43. As aresult of this bevel the space between the cover and shield surfaces is enlarged and the formation of a capillary path beyondl this point prevented. v

The shielding Lof the spark' plug is completed by means of cover I3 which surmounts interme diate shield l2. Said cover is formed of an ele' c trically conductive metal and comprises a hollow housing which may be of sheet metal and is adapted to snugly nt around shield l2 and to 'be removeably secured thereto. An annularrib terial` of the cover. In :order to impart a degree of resiiiency tothe material of the cover .adjacent to said rib a series of circumferentially spaced slits 46 are formed in the material of the `cover along the lower portion thereof; :said slits ter-- minating below .the `upper edge of shield I2. As a. result oi this arrangement the cover may be securely positioned on shield .It and readily removed therefrom and replaced thereon; Vthe resilient or yielding action of the lower portion `of the cover permitting this to be accomplished.

A modied forni of cover is shown in Figure 4 wherein a series of `tongues 41 are formed in the material of the cover. Said tongues are provided with indentations 48 which form ribs on the in ternal surface of the cover adapted to be .engaged in the complementary annular groove 44 'formed in the shield. In order to permit the introduction of an ignition cable into the interior thereof, as will more clearly appear hereafter cover I3 is formed with a perforation 52 in its upper wall portion, said perforations 'being provided with indentation 55 and internally extending annular flange 51.

Positioned within cover I3 is cover insulator 49 which may be formed of a phenolic, ceramic or similar insulating material. Said cover insulator is formed with a depending post 5i] which is adapted to be received in the interior of cavity 34 in insulator 23 and in spaced relation to the Wall of said cavity. It should be noted that the upper end of the insulator Z3 abuts upon the lower end surface of cover insulator te when said cover is in position, and that said cover .insulator is provided with an annular depending flange 5I which rests immediately above the beveled end 43 of shield I2. The upper end of said shield lies below the level of the upper end of insulator 23. As a. result of this arrangement any .moisture or water which may enter the spark plug under pressure will collect in the space between insulator 23 and shield I2, and be trapped therein. In the event that Such water reaches the level of flanges 5| it will flow out over the upper end 43 of the shield and out of the plug through the space provided between the cover and the bevel on the shield. The entry of any water into cavity 34 is thus prevented.

Cover insulator 49 is further provided with an axial bore 52 which extends through depending post 5i) and communicates with transverse bore 53 formed in the upper portion of said insulator. Axial bore 52 is enlarged and threaded at its lower end to threadedly receive contact screw 55. The upper end of said contact screw is tapered to a point in order to permit the end thereof to pierce the insulation of an ignition cable as will more clearly appear hereafter. Transverse bore 53 extends part way only into said .insulatorI and terminates somewhat beyond the point at which it is entered by contact screw 55 as shown by the broken line in Figure l. The opening of said transverse bore is enlarged and threaded; registering with the perforation in the wall .of cover I3.

The cover assembly is completed by means of terminal tube I 4. Said tube is provided with a restricted inner end portion which is threaded and adapted to be threadedly engaged with the threads formed in transverse bore 53. By reason of the restriction of the forward portion of said tube a shoulder is formed lwhich is adapted to abut upon internal flange 5T formed in perforation 58 oi the cover. The terminal tube fits into the perforation and against flange 51 thereof 6. in a snug manner. Thus whenthe tubes-nd cover insulator are threadedly engaged the cover insulator is drawn against the interior wall oi the cover and the tube shoulder is drawn against ilange 5l. As a result of this arrangement the cover insulator is firmly secured in position and a water tight seal is provided between the cover and the tube. In order to provide an additional mechanical and electrical seal and to further secure the parts to each other an insulating varnish or cement is applied to the threads of the parts immediately prior to their threaded engagement with each other. A silicone resin may advantageously be utilized for this purpose. The bore of the terminal tube I4 is adapted to receive ignition cable I5. The outer end of the bore in said tube is restricted at 59 in order to iirmly grip the cable which is inserted therein and to provide a. tight seal therewith in addition to preventing its displacement therefrom. In the assembly of said cover terminal tube I4 is threads edly engaged with cover insulator t! as heretofore indicated and ignition cable l5 is inserted into the tube the end of said cable passing into lthe transverse bore of said cover insulator. Contact screw 55 is then threaded into axial bore 52. As said contact screw is tightened the pointed end thereof pierces the insulation of the ignition. cable and makes electrical contact therewith, in addition to preventing the withdrawal of the cable. Cover I3 may then be positioned upon shield I2 whereupon the upper end of the helical spring 4I makes contact with the head of the contactl screw and completes the electrical circuit of the spark: plug. When it is desired to remove or replace the ignition cable it is merely necessary to remove the cover and retract contact screw 55. The head of said screw is provided with 'a slot which is suiiciently large to receive a coin in addition to the blade of a screw driver thereby permitting the replacement of said cable without the use of special tools. Upon the retraction of the screw the cable is removed and a new cable may be inserted. The insulation on the cable need not be removed. The Contact screw is then re-threaded into the bore and by piercing the cable insulation makes contact with the conductor therein. The cover may then be replaced.

A modified form of cover arrangement; parw ticularly adapted for use with an ignition cable provided with a shielded braid or sheath, is shown in Figure 3. In this modified form, cover I3 is provided with a perforation 553 which is adapted to snugly receive a metallic sleeve 6I. Said metallic sleeve is provided with flange t2 adapted to abut upon shoulder $3 of terminal tube Bid. Said terminal tube is secured to the cover .insulator in the manner heretofore indicated. The metallic sleeve E! is soldered or braced to the walls of the perforation in the cover. A metallic collar 65 is provided, to which the metallic braid covering the ignition cable, is secured as by soldering. Collar $5 and sleeve tI are firmly se cured to each other by means of collar nut 5S. By reason of this arrangement continuous shieldi ing is provided between the metallicsheath or braid of the ignitioncable and the spark plug.

I have here shown and described preferred embodiments of my invention. It will be apparent, however, that this invention is not limited to these embodiments and that many changes, additions and modiiications can be made in connection therewith without departing from the spirit and scope of the invention as herein disclosed and hereinafter claimed.

Having describedV my invention, what I claim as new and desire to secure by Letters Patent is:

1. Ina spark plug having va shell adapted to be secured to the body of an internal combustion engine; an electrode carried by said shell, an insulator having a cavity therein carried by said shell, an electrode adapted to cooperate with said rst electro-de to form a spark gap, secured within said insulator, a helical spring located within said cavity in electrical contact with the upper end of said second electrode, an intermediate shield member secured to said shell and adapted to clamp said insulator in position, a cover adapted to detachably surmount said shield and provided with a perforation therein which is surrounded by an internally extending sleeve and flange; a complementary cover insulator positioned in said cover and provided with a depending post adapted to be received in the cavity of said first insulating member and a depending circumferential ange extending below the upper end thereof; a contact screw adapted to be threadedly received in an axial bore provided in said post and having a pointed end extending into a transverse bore provided in the upper portion of said cover insulator, the other end of said screw being adapted to make electrical contact with said `helical spring; a terminal tube having an axial perforation adapted to receive an ignition cable anda reduced end portion adapted, to be threadedly received in the opening of said transverse bore thereby introducing the end of said cable into the portion of said transverse bore entered by the contact screw and securing said cover insulator in position within said core.

2. In a spark plug having a shell adapted to be secured to the body of an internal combustion engine; an electrode carried by said shell, an insulator having a cavity therein carried by said shell, a center electrode adapted to cooperate with said first electrode to form a spark gap secured within said insulator; an intermediate shield member secured to said shell; a cover adapted to detachably surmount said shield and provided with a perforation in the wall thereof whichis surrounded by an internally extending sleeve and flange; a complementary cover insulator positioned in said cover; a contact screw adapted to be threadedly received in an axial bore provided in said cover insulator and having an end extending into a transverse bore provided in the upper portion thereof, the other end of said screw being adapted to make electrical contact with said center electrode, a terminal tube havingan axial perforation adapted to receive an ignition cable and a reduced end portion adapted to be threadedly received in the opening of said transverse bore thereby introducing the end of said cable into the portion of said transverse bore entered by the contact screw and securing said cover insulator in position within said core.

3. In a spark plug having a shell adapted to be secured to the body of an internal combustion engine; an electrode carried by said shell, an insulator having a cavity therein carried by said shell, an electrode adapted to cooperate with said first electrode to form a spark gap secured within said insulator, a helical spring located within said cavity in electrical contact with the upper end of said second electrode, an intermediate shield member secured to said shell and adapted to clamp said insulator in position, a cover adapted to detachably surmount said shield and provided with a perforation therein which is surrounded by an internally extending slve and iiange; a complementary cover insulator positioned in said cover and provided with a depending post adapted to be received in the cavity of said first insulating member whereby the lower end surface of said cover insulator abuts With the upper end surface of said rst insulator; a contact screw adapted to be threadedly received in an axial bore provided in said post and having a pointed end extending into a transverse bore provided in the upper portion of said cover insulator, the other end of said screw being adapted to make electrical contact with said helical spring; a terminal tube having an axial perforation adapted to receive an ignition cable and a reduced end portion adapted to be threadedly received in the opening of said transverse bore thereby introducing the end of said cable into the portion of said transverse bore entered by the contact screw and securing said cover insulator in position within said core.

4. 'The device according to claim 3 wherein a depending flange is provided on said cover insulator adapted to surround the upper end of said first insulator.

5. The device according to claim 3 wherein a depending iiange is provided on said cover insulator adapted to surround the upper end of said first insulator, the end surface of said flange being adapted also to abut with the upper edge of said intermediate shield.

6. The device according to claim 3 wherein the upper end of the intermediate shield member is tapered so as to provide an enlarged space between said intermediate shield and the interior surface of said cover.

7. In a spark plug having a shell adapted to be secured to the body of an internal combustion engine; an electrode carried by said shell, an insulator having a cavity therein carried by said shell, an electrode adapted to cooperate with said first electrode to form a spark gap secured within said insulator, a helical spring located within said cavity in electrical contact with the upper endof said second electrode, an intermediate shield member secured to said shell and adapted to clamp said insulator in position, the upper portion of said intermediate shield being spaced from said insulator to provide an air space therebetween and the upper end of said intermediate shield being tapered, a cover adapted to detachably surmount said shield in telescopic relation therewith, the tapered upper end of said shield comprising an interruption of any capillary path for moisture between said cover and said shield, said cover being provided with a perforation therein which is surrounded by an internally extending sleeve and flange; a complementary cover insulator positioned in said cover and provided with a depending post adapted to be received in the cavity of said first insulating member and a depending circumferential flange extending below the upper end there-- of; a contact screw adapted to be threadedly Ireceived in an axial bore provided in said post and having a pointed end extending into a transverse bore provided in the upper portion oi said cover insulator, the other end of said screw being adapted to make electrical contact with said helical spring; a terminal tube havingan axial perforation adapted to receive an ignition cable and a reduced end portion adapted to be threadedly received in theopening of said transverse bore thereby introducing the end of said cable into the portion of said transverse bore entered by the contact screw and securing said cover insulator in position Within said cover.

MAXWELL INGRAM.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date Pieper May 27, 1930 Rohde Nov. 25, 1930 Number 10 Name Date James Sept. 19, 1933 Paulson Oct. 10, 1933 Mascuch Apr. 12, 1938 Burrell et a1 Jan. 26, 1943 Johanson Aug. 8, 1944 Hastings Jr. et al. Aug. 15, 1944 Setterblade Feb. 6, 1945 Carlson Dec. 25, 1945 Hensel Dec. 25, 1945 Robertson Apr. 30, 1946 Van Orden Mar. 8, 1949 

